Method and instruments for inserting modular implant components

ABSTRACT

An instrument is disclosed for inserting a modular implant, the instrument comprising a first end and a second end, the first end having engagement means for engaging a stem component of the modular implant, the engagement means comprising separation means for separating a body component of the modular implant and the stem component from one another so as to permit rotational positioning of the body component and the stem component relative to one another.

REFERENCE TO PENDING PRIOR PATENT APPLICATION

This patent application claims benefit of pending prior U.S. ProvisionalPatent Application Ser. No. 60/378,986, filed May 9, 2002 by Steven C.Pubols et al. for METHOD FOR INSERTING MODULAR IMPLANT COMPONENTS, whichpatent application is hereby incorporated herein by reference.

FIELD OF THE INVENTION

This invention is related to modular orthopedic apparatus and methods ingeneral, and more particularly to apparatus and methods for insertingmodular implant components.

BACKGROUND OF THE INVENTION

The aim of Total Hip Arthroplasty (THA) is the reduction of pain and therestoration of function to a diseased hip joint via the substitution ofengineered materials for the diseased tissue. Successful outcomes dependlargely on the proper sizing, placement and orientation of the implant.Incorrect biomechanics (e.g. joint reaction forces, soft tissuebalancing) can slow or prevent healing, cause gait abnormalities andlead directly to early implant failure.

There are three portions to the femoral side of a total hip prosthesis:the neck, body, and stem. In a one piece hip design, all three of theseportions are a part of a solid construct. As a solid construct, theorientation of each portion with respect to one another is fixed andunchangeable. A surgeon implants one of these solid construct devices byattaching a handle or holder to the prosthesis and then driving it intoa prepared opening in the bone. The orientation of the neck and stem iscontrolled by, and limited to, the orientation of the prepared openingin the bone.

With the invention of two-piece designs, specifically U.S. Pat. No.4,846,839, issued to Noiles, incorporated herein by reference, andsubsequently marketed and sold by DePuy, A Johnson and Johnson Company,under the “S-ROM Hip System” tradename, a surgeon is given theopportunity to independently orient the position of the implant bodyapart from the rotation or anteversion of the neck. In these designs,the stem and neck of the implant are a one-piece component and the bodyof the implant is a separate component. These devices also incorporateflutes or spines on the stems of the implant so as to provide additionalresistance to rotation. These spines engage the bone during the initialfew inches of insertion into the femoral canal, forcing the finallocation of the implant neck to be totally dependent on the initialinsertion orientation of the distal stem. If the stem is fully insertedand the neck is incorrectly oriented, the entire implant must beremoved, indexed, and reinserted. This iterative approach to neckplacement is time consuming, damages the bone/implant interface, andresults in the loss of implant stability. This problem is compoundedwhen a bowed stem is used in place of a straight stem. The bow in thestem will follow the natural bend in femoral canal, which in turndictates the final position of the femoral neck. Using two-piece modularimplants, where the first piece is a neck with curved stem component andthe second piece is the body component, a surgeon is given no choice oroption for the femoral neck orientation with respect to the orientationof the bowed or curved stem.

With a three-piece modular implant, there is provided a stem component,a neck component, and a body component which are independent of oneanother and are independently adjustable with respect to one another.With insertion, the stem component and body component each seek a bestfitting position within the femoral canal. Following insertion, the neckcomponent can be oriented by a surgeon in order to establish optimaljoint and motion mechanics.

Prior to insertion of an actual implant, the use a mock implant or“trial” is desirable as a means of evaluating correct size andpositioning. A surgeon uses the measurements taken from the trialimplant so as to select the final implant components. A trial stem isgenerally smaller than an implant stem and is configured without spinesor flutes so as to aid in the insertion and removal of the trial withoutdamaging the bone/implant interface. When inserted into the preparedcavity in the bone, the stem component will follow the path of leastresistance so long as its motion is not restricted otherwise. For thisreason, it is advantageous to allow the implant stem rotational freedomwith respect to the body when inserting the final implant. Although itis desirable for the stem component to be rotationally free duringinsertion, it is important for the stem component to be properly alignedwith the body and neck components so as to ensure proper final assembly.Without this alignment, the stem may be off axis, making it difficult orimpossible to assemble the neck and body segments along an axis.

Other methods for implanting two-piece or three-piece modular deviceswhere the stem component is separate from the body and/or neckcomponent(s) include inserting the stem component until it is proud ofits intended final position and then using the body component to seatthe stem by impaction. For example, a two-piece system having separatestem and combination body/neck components is manufactured and sold bythe Biomet Corporation, under the “Impact Hip System” tradename. Forfurther example, a three-piece system having separate stem, body, andneck components is manufactured and sold by the Exactech Corporation,under the “Accumatch M-Series Hip System” tradename. In both examples,impaction of the body onto the stem also serves to secure the stem andbody assembly. One disadvantage of this method is that stem/bodyorientation must be determined visually prior to full seating and mayshift during implantation. Another disadvantage is that the assemblyforce is equivalent to the resistance of the stem sliding down thecanal. If the stem moves in the canal during final assembly, the stemmay be driven too deeply into the canal causing surgical delays, or thestem and body will not be tightly assembled, leading to fretting,corrosion, and early failure of the construct.

SUMMARY OF THE INVENTION

An object of the invention is to provide an instrument for inserting amodular implant in which the instrument allows the rotationalpositioning of the body component, neck component and stem componentrelative to one another.

Another object of the invention is to provide an instrument forinserting a modular implant which allows rotational positioning of aneck and body component relative to a stem component.

A further object of the invention is to provide a system for inserting amodular implant in which the insertion tool provided with the bodycomponent and the stem component allows positioning of the bodycomponent and the stem component relative to one another.

With the above and other objects in view, as will hereinafter appear,there is provided an instrument for inserting a modular implant, theinstrument comprising a first end and a second end, the first end havingengagement means for engaging a stem component of the modular implant,the engagement means comprising separation means for separating a bodycomponent of the modular implant and the stem component from one anotherso as to permit rotational positioning of the body component and thestem component relative to one another.

This invention provides for an improved apparatus and method ofinserting or implanting a modular orthopedic prosthesis. The improvedapparatus and method allows the components of the implant to beassembled together and inserted into the femur without the need for themodular connections to be locked together, thereby permitting eachcomponent to seek its best fitting position within the canal. Further,this permits the orientation of the neck component relative to the bodyand stem after they have achieved this best fitting position. Theimplant neck, body, and stem may rotate freely with respect to oneanother until the components are fully seated in the bone. The resultsin improved alignment between the implant and the bone, which in turnreduces the time and force required to implant the prosthesis. Forexample, this method may be used in implanting hip, shoulder, and kneeprostheses.

In accordance with a further feature of the invention there is provideda system for inserting a modular implant, the system comprising: a bodycomponent having a neck segment extending therefrom, and the bodycomponent forming a bore and counterbore therein; a stem componenthaving a threaded end configured for selective disposal within the boreand counterbore so as to expose through the counterbore a given lengththereof; and an insertion tool comprising a first end and a second end,the first end forming a threaded recess for engaging the stem componentof the modular implant, the threaded recess having a depth less than thelength of the threaded end so as to permit rotational positioning of thebody component and the stem component relative to one another.

The present invention improves upon existing techniques by allowing forthe complete (fully seated) implantation of the stem and body whilemaintaining rotational freedom between the stem, body, and neckcomponents. Alternatively, the surgeon may elect to assemble the neckand body at the desired orientation as determined during the trialingphase of surgery. A method of a preferred embodiment of the presentinvention allows for the stem to be held securely during insertion,while the neck and body assembly may rotate freely about the stempositioning in order to seat the stem in a best fitting position. Oncethe body is fully seated, the driver may be removed and the implants maybe fully assembled using an assembly tool or another instrument. Thepresent invention is not limited to the use of three-piece designs. Thepresent invention may be used in a two-piece design where the neck andbody portions of the implant are manufactured as a one-piece component.

The above and other features of the invention, including various noveldetails of construction and combinations of parts and method steps willnow be more particularly described with reference to the accompanyingdrawings and pointed out in the claims. It will be understood that theparticular devices and method steps embodying the invention are shown byway of illustration only and not as limitations of the invention. Theprinciples and features of this invention may be employed in various andnumerous embodiments without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore fully disclosed or rendered obvious by the following detaileddescription of the preferred embodiments of the invention, which are tobe considered together with the accompanying drawings wherein likenumbers refer to like parts, and further wherein:

FIG. 1 is a schematic illustration of one form of a modular implantsystem including a modular implant and an insertion tool; and

FIG. 2 is a schematic illustration of another form of a modular implantsystem including a unitary body/neck component for use with theinsertion tool.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, and in a preferred embodiment of the presentinvention, there is shown a three-piece modular implant system 1. Thisthree-piece modular implant of modular implant system 1 comprises a bodysegment 2, a neck segment 3 with a counterbore 4, and a stem segment 5with a threaded end 6 and a taper 7. Threaded end 6 has a length toextend above the surface of counterbore 4 by a predetermined distance.Modular implant system 1 further comprises an insertion tool 8 withthreaded hole 9. Hole 9 has a shorter depth than the predetermineddistance of threaded end 6 extending above the surface of counterbore 4.Accordingly, when insertion tool 8 is threaded onto threaded end 6 a gapremains between the proximal surface of counterbore 4 and the distal endof insertion tool 8. When the proximal end of insertion tool 8 isimpacted, taper 7 is forced out of engagement with the mating surface ofbody segment 2 so that neck segment 3 remains rotationally free.

In another preferred embodiment of the present invention (FIG. 2) thereis provided a unitary component comprising a modular body/neck component10 and a modular stem component 5.

1. An instrument for inserting a modular implant, the instrumentcomprising: a first end and a second end, the first end having a stemengagement feature for engaging a stem component of a modular implantand a body engagement feature for engaging a body component of a modularimplant, the stem engagement feature and the body engagement featurebeing so disposed as to maintain a separation between an implant bodycomponent and an implant stem component when the engagement features arein contact with their respective components so as to permit rotationalpositioning of the body component and the stem component relative to oneanother
 2. An instrument for inserting a modular implant according toclaim 1 wherein the second end of the instrument has an impaction site,and further wherein the body component and the stem component aredisengaged from one another by applying a force to the impaction site.3. An instrument for inserting a modular implant according to claim 1wherein the stem engagement feature comprises a threaded recess and oneend of the stem component comprises a threaded end, the threaded end andthe threaded recess configured to threadably engage one another, wherethe depth of the stem engagement feature is less than the length of thethreaded end of the stem that is exposed above the engagement surface onthe body when the implant is assembled together.
 4. An instrument forinserting a modular implant according to claim 1 wherein the stemengagement feature comprises a threaded protrusion and one end of thestem component comprises a threaded recess, the threaded recess and thethreaded protrusion configured to threadably engage one another, wherethe length of the stem engagement feature is greater than the depth ofthe engagement surface on the stem below the engagement surface on thebody when the implant is assembled together.
 5. An instrument forinserting a modular implant according to claim 1 wherein the stemengagement feature and the body engagement feature act to align theimplant body and implant stem.
 6. An instrument for inserting a modularimplant, the instrument comprising: a first end and a second end, thefirst end having a stem engagement feature for engaging a stem componentof a modular implant and a neck engagement feature for engaging a neckcomponent of a modular implant, the stem engagement feature and the neckengagement feature being so disposed as to maintain a separation betweenan implant neck component and an implant stem component when theengagement features are in contact with their respective components soas to permit rotational positioning of the neck component and the stemcomponent relative to one another
 7. An instrument for inserting amodular implant according to claim 6 wherein the second end of theinstrument has an impaction site, and further wherein the neck componentand the stem component are disengaged from one another by applying aforce to the impaction site.
 8. An instrument for inserting a modularimplant according to claim 6 wherein the stem engagement featurecomprises a threaded recess and one end of the stem component comprisesa threaded end, the threaded end and the threaded recess configured tothreadably engage one another, where the depth of the stem engagementfeature is less than the length of the threaded end of the stem that isexposed above the engagement surface on the neck when the implant isassembled together.
 9. An instrument for inserting a modular implantaccording to claim 6 wherein the stem engagement feature comprises athreaded protrusion and one end of the stem component comprises athreaded recess, the threaded recess and the threaded protrusionconfigured to threadably engage one another, where the length of thestem engagement feature is greater than the depth of the engagementsurface on the stem below the engagement surface on the neck when theimplant is assembled together.
 10. An instrument for inserting a modularimplant according to claim 6 wherein the stem engagement feature and theneck engagement feature act to align the implant neck and implant stem.11. An instrument for inserting a modular implant, the instrumentcomprising: a first end and a second end, the first end having a stemengagement feature for engaging a stem component of a modular implantand a main implant engagement feature for engaging a main implantcomponent of a modular implant, the stem engagement feature and the mainimplant engagement feature being so disposed as to maintain a separationbetween an implant main implant component and an implant stem componentwhen the engagement features are in contact with their respectivecomponents so as to permit rotational positioning of the main implantcomponent and the stem component relative to one another
 12. Aninstrument for inserting a modular implant according to claim 11 whereinthe second end of the instrument has an impaction site, and furtherwherein the main implant component and the stem component are disengagedfrom one another by applying a force to the impaction site.
 13. Aninstrument for inserting a modular implant according to claim 11 whereinthe stem engagement feature comprises a threaded recess and one end ofthe stem component comprises a threaded end, the threaded end and thethreaded recess configured to threadably engage one another, where thedepth of the stem engagement feature is less than the length of thethreaded end of the stem that is exposed above the engagement surface onthe main implant when the implant is assembled together.
 14. Aninstrument for inserting a modular implant according to claim 11 whereinthe stem engagement feature comprises a threaded protrusion and one endof the stem component comprises a threaded recess, the threaded recessand the threaded protrusion configured to threadably engage one another,where the length of the stem engagement feature is greater than thedepth of the engagement surface on the stem below the engagement surfaceon the main implant when the implant is assembled together.
 15. Aninstrument for inserting a modular implant according to claim 11 whereinthe stem engagement feature and the main implant engagement feature actto align the implant main implant and implant stem.
 16. A method forinserting a modular implant, the instrument where: an instrument isprovided comprising: a first end and a second end, the first end havinga stem engagement feature for engaging a stem component of a modularimplant and a body engagement feature for engaging a body component of amodular implant, the stem engagement feature and the body engagementfeature being so disposed as to maintain a separation between an implantbody component and an implant stem component when the engagementfeatures are in contact with their respective components so as to permitrotational positioning of the body component and the stem componentrelative to one another
 17. A method for inserting a modular implantaccording to claim 16 wherein the second end of the instrument has animpaction site, and further wherein the body component and the stemcomponent are disengaged from one another by applying a force to theimpaction site.
 18. A method for inserting a modular implant accordingto claim 16 wherein the stem engagement feature comprises a threadedrecess and one end of the stem component comprises a threaded end, thethreaded end and the threaded recess configured to threadably engage oneanother, where the depth of the stem engagement feature is less than thelength of the threaded end of the stem that is exposed above theengagement surface on the body when the implant is assembled together.19. A method for inserting a modular implant according to claim 16wherein the stem engagement feature comprises a threaded protrusion andone end of the stem component comprises a threaded recess, the threadedrecess and the threaded protrusion configured to threadably engage oneanother, where the length of the stem engagement feature is greater thanthe depth of the engagement surface on the stem below the engagementsurface on the body when the implant is assembled together.
 20. A methodfor inserting a modular implant according to claim 16 wherein the stemengagement feature and the body engagement feature act to align theimplant body and implant stem.
 21. An instrument for inserting a modularimplant, the instrument comprising: a first end and a second end, thefirst end having a stem engagement feature for engaging a stem componentof the modular implant and a body engagement feature for engaging a bodycomponent of the modular implant, the second end having an impactionfeature for applying a force to the instrument, the stem engagementfeature and the body engagement feature being configurably disposed soas to maintain a separation between the body component and the stemcomponent so as to permit rotational positioning of the body componentand the stem component relative to one another.
 22. An instrument forinserting a modular implant according to claim 21 wherein the second endof the instrument has an impaction site, and further wherein the bodycomponent and the stem component are disengaged from one another byapplying a force to the impaction site.
 23. An instrument for insertinga modular implant according to claim 21 wherein one end of the stemcomponent comprises a threaded end extending from the stem component andthe stem engagement feature forms a threaded recess, the threaded endand the threaded recess configured to threadably engage one another,wherein the distance between the stem engagement feature and the bodyengagement feature is less than the distance between the engagementsurface on the stem and the engagement surface on the body when theimplant is assembled together.
 24. An instrument for inserting a modularimplant according to claim 21 wherein an end of the stem componentcomprises a threaded recess extending into the stem component and thestem engagement feature forms a threaded protrusion, the threaded recessand the threaded protrusion configured to threadably engage one another,wherein the distance between the stem engagement feature and the bodyengagement feature is greater than the distance between the engagementsurface on the stem and the engagement surface on the body when theimplant is assembled together.
 25. An instrument for inserting a modularimplant according to claim 21 wherein the stem component comprises athreaded end extending therefrom and the stem engagement feature forms athreaded recess, the threaded end and the threaded recess configured tothreadably engage one another, where the distance between the stemengagement feature and the body engagement feature is less than thedistance between the engagement surface on the stem and the engagementsurface on the body.
 26. An instrument for inserting a modular implantaccording to claim 21 wherein the second end of the instrument has animpaction site, and further wherein the body component and the stemcomponent are disengaged from one another by applying a predeterminedforce to the impaction site.
 27. An insertion tool for inserting amodular implant according to claim 21 wherein the second end of theinstrument has an impaction site, wherein the body component and thestem component are disengaged from one another by applying apredetermined force to the impaction site.
 28. An insertion tool forinserting a modular implant of the type comprising a body componenthaving a neck segment extending therefrom, and the body componentforming a bore and counterbore therein, and a stem component having athreaded end configured for selective disposal within the bore andcounterbore so as to expose through the counterbore a given lengththereof, the insertion tool comprising: a first end and a second end,the first end forming a threaded recess for engaging the stem componentof the modular implant, the threaded recess having a depth less than thelength of the threaded end so as to permit rotational positioning of thebody component and the stem component relative to one another.
 29. Aninsertion tool for inserting a modular implant according to claim 28wherein the body component comprises a unitary body segment and necksegment.
 30. An insertion tool for inserting a modular implant accordingto claim 28 further comprising a neck component configured toselectively attach to the body component.
 31. An instrument forinserting a modular implant, the instrument comprising: a first end anda second end, the first end having a stem engagement feature forengaging a stem component of the modular implant and a neck engagementfeature for engaging a neck component of the modular implant, the secondend having an impaction feature for applying a force to the instrument,the stem engagement feature and the neck engagement feature beingconfigurably disposed so as to maintain a separation between the neckcomponent and the stem component so as to permit rotational positioningof the neck component and the stem component relative to one another.32. An instrument for inserting a modular implant, the instrumentcomprising: a first end and a second end, the first end having a stemengagement feature for engaging a stem component of the modular implantand a main implant engagement feature for engaging the main component ofthe modular implant, the second end having an impaction feature forapplying a force to the instrument, the stem engagement feature and themain implant engagement feature being configurably disposed so as tomaintain a separation between the main implant component and the stemcomponent so as to permit rotational positioning of the main implantcomponent and the stem component relative to one another.